There’s something about how the Viper slithers into combat in XCOM 2 that just grabs you. So to speak. We sat down with Greg Foertsch and Dennis Moellers, the Art Director and Lead Animator for XCOM 2, to talk more about the animation that goes into bringing the aliens to life.

How much time went into perfecting the movement – and how difficult was it – for the aliens in XCOM 2?

Moellers: I don’t know if we ever stopped. It’s an on-going process to nail every animation down for every unit. Sometimes a new weapon or ability gets added and it affects several different units. Each of these units will then need new animations to react accordingly. What helps is that every unit in XCOM has so much personality behind it already that it makes creating their movements that much easier. We also have a passionate team of artists who have an endless supply of awesome ideas as to what these creatures and soldiers should be doing.

So, what would you say was the most challenging alien to animate, then?

Moellers: The Viper was one of the most challenging because we had less real world reference to go on. With the Viper it was more about trying different ideas until we hit upon what worked. We would come up with an idea and block-in the action, then take a look at it as a team and decide if it felt right. It was a challenge to work from scratch like that, but once we knew the right direction to go in, the rest came quickly.

Walk us through that process. What were some of the considerations when animating a snake-creature into an anthropomorphized hybrid?

Moellers: It took us a while to figure how to balance the motion of the snake tail with the human upper body. I remember some trial and error with the run cycle. When a snake slithers it keeps its head close to the ground, but the Viper needs to keep its torso upward. Getting the right amount of tail movement along with the torso movement was a difficult balance. Too much movement made it look out-of-control, but too little made it look stiff. Once we found that balance I was really happy with the final result.

What were some of the inspirations for the looks, feel and movement of the Viper – besides the obvious?

Moellers: Other than the typical snake footage, we studied Medusa from both the original and remake of ‘Clash of the Titans’. It was a good starting point to see how they combined the snake and human form. Also, I wanted the Viper to feel unnerving and the best way to accomplish this was with the speed of its movements. It’s great to see how quickly it can slither along the ground and slide into cover, ready to take out your next soldier.

Snakes – and Snakemen – have been a big part of the XCOM series for some time now. Can you talk about the evolution of it within the series?

Foertsch: The idea to go full snake with the Viper in XCOM 2 has to do with the narrative of the game mixed with honoring the history of XCOM. In Enemy Unknown, the (not so) subtle secret behind the Thin Man was they were the original X-COM’s Snakemen in disguise. This fit with Enemy Unknown’s story because the aliens were invading and needed an infiltration unit. In XCOM 2, the aliens have won and there’s less of a need to hide so the snake unit came back. We also knew the Snakeman was a fan favorite that would pair well with the sequel’s more visceral style.

Speaking of fan favorites, what do you make of the fan reactions to the animations and overall design of the Viper?

Foertsch: We’re very happy that the fans seem to have taken so well to the Viper. Every day we see someone on our forums or hitting us up on Twitter letting us know a Viper slithered out of the shadows, grabbed a soldier out of cover using its tongue, and strangled them to death. If the Viper is killing your soldiers, we did our job.

Let’s talk about one of the other mainstays of the series, Mutons. How do you feel they’ve been represented so far and how they’ve evolved in the past two games?

Foertsch: The Muton is my favorite alien from XCOM 2, but they’re a tough unit to redesign for each game. You don’t want to change them too much because everyone has expectations for what it should look like, but they need to evolve with the narrative and game design. This is where animation can be extremely valuable. The animation can highlight or even draw out a completely new personality. The Mutons in Enemy Unknown were primal and gorilla-like in their posture and their chest thumping animations. In XCOM 2, Mutons are leaner and act more like badass tough-as-nails soldiers who may have taken one too many steroid injections.

Well, if you’re making them more human with DNA splicing, you certainly have more references for modeling them.

Foertsch: Slimming them down also let us deliver a new interesting take on the Muton while at the same time staying true to the look. Mutons have always had a very animalistic design and behavior. XCOM 2 saw the aliens becoming a little more human, but we still wanted those familiar character traits to show. Each alien unit, including the Mutons, retains some of their primal animations which you get glimpses of as you play.

By a quick comparison, what was your target for modelling movement with the new Berserkers – compared to the Mutons?

Moellers: I wanted the Berserker to feel very different from the Muton. Much more animalistic and wild. The first character I thought of was a hulking monster - crazy, barely able to stay in one place. Then the animators layered on movement inspired by bears or apes, like when the Berserker stops running and smashes its fists to the ground.

So then what is the animation process like for something that is essentially formless - like the Faceless?

Foertsch: The Faceless was an awesome enemy to animate. The concept behind the enemy was so strong that it gave us plenty to work with. We knew this alien was a huge and formless creature who may or may not even have bones. To us, this meant Faceless should move deceptively slow and usually only one limb at a time. The creepiness of the slow and sloppy movement is then intensified when the Faceless climbs through a tiny window and suddenly starts charging at full height.

What do you consider when animating any alien for an XCOM game and what lessons have you learned from the work done on XCOM 2?

Foertsch: The secret is having lots of reference, doing a lot of movement study, and having a vision in your head before we sit down at our PCs. Even with a game about a fictional future with monsters and aliens running around, there’s still lots of reference out there. We have to find what’s out there in the world and connect it back to the game. When someone notices a similarity between how a Berserker moves and a charging bull, that’s a good thing. It helps the player identify with the unit, makes it more believable and conveys information. The Muton only needs to take one step for a player to realize what this enemy is about.